Abnormal Breathing Sounds – Types and Causes

Abnormal breathing sounds differs in quality from the normal hollow, rustling sound that is heard as air passes through the large airways like the pharynx, larynx and trachea (bronchial breathing) and resonates in the bronchial tree and lungs (vesicular breathing).

Abnormal sounds may resemble a musical wind instrument or be more rough in quality like a grating noise. Some conditions may cause crackling, creaking, bubbling or even clicking breathing sounds. Identifying the type of abnormal breath sound is important to assist with a diagnosis.

More than one type of abnormal sound may be present at the same time. Since the causes may overlap, other criteria as well as further diagnostic testing may be necessary for a final diagnosis.


Breathing sounds that are louder or softer than normal, without any change in quality (abnormal sounds), may be due to other causes discussed under Noisy Breathing.

Types of Abnormal Breath Sounds

What is wheezing?

Wheezing describes breathing sounds that are more musical in nature than normal breathing sounds – bronchial and vesicular breathing. It is either high pitched or low pitched.

A high pitched wheeze may be indicative of pathology within the smaller airways like the bronchioles, while a low pitched wheeze may be due to pathology within the larger airways like the main bronchi. However, the site of the pathology may not always cause these differences in pitch.

Wheezing indicates that the airway is narrowed, either by a solid mass, mucus plug, bronchospasm or bronchial wall swelling. The narrowing may be more prominent upon expiration (breathing out) than inspiration.

For more information on conditions that may result in wheezing, refer to causes of wheeze.

The most common causes of wheezing is asthma and COPD (emphysema or chronic bronchitis). These conditions result in episodes of wheezing with sounds of varying pitch and volume. Causes of wheezing like lung cancer usually results in a wheeze that is continuous and does not differ significantly in pitch since the obstruction is fixed.

What is a stridor?

A stridor is a monotone whistling noise that is high pitched and often mistaken for a wheeze. It can vary from being musical in tone to rough and raspy and in most cases, it is more pronounced upon inspiration (breathing in).

A stridor indicates a partial obstruction usually in the upper respiratory airways (pharynx, larynx) and upper part of the trachea. Due to vocal resonance, it may also be heard in the chest, however, it is loudest over the throat and is often audible without a stethoscope.

The various conditions that may result in a stridor are further discussed under causes of stridor.

The most common cause of a stridor is inflammation of the upper respiratory tract (pharyngitis, laryngitis, tracheitis) usually due to an infection. A foreign object lodged in the upper respiratory tract or an abscess may also cause a stridor. Less common causes include vocal cord paralysis or laryngospasm.

What is a crackle?

Crackles are loud, popping or snapping sounds that are almost explosive in nature and most prominent upon inspiration (breathing in). It is non-musical and discontinuous often interrupted by normal breathing or even other abnormal breath sounds.

Crackles usually indicate a collapse of the distal airways which rapidly open when air enters the respiratory tract upon inspiration thereby causing a crackling noise. Another cause for crackles is when air enters the lung and bubbles in secretions, either fluid in the lungs or mucus. It has more of a bubbling sound in these cases.

Causes of Crackles

The cause of the crackles can be partly identified by when it is heard during inspiration. Some of the causes include :

  • Bronchiolitis – heard early in inspiration.
  • Bronchiectasis -rough inspiratory and expiratory crackles
  • Pulmonary edema – crackles of a bubbling nature more prominent in mid-inspiration
  • Pulmonary fibrosis – heard late in inspiration (towards the end of inhalation)
  • Tuberculosis (TB) – bubbling sound
  • Asthma – bubbling sound with wheeze
  • Bronchitis – bubbling sound with occasional wheeze
  • Pneumonia – bubbling or crackling noise
  • COPD – coarse, sometimes bubbling noise
  • Lung abscess – grating noise, often with wheeze or stridor depending on the location

What is a pleural friction rub?

A pleural rub is a squeaking or creaking sound like a stiff object creaking under stress. It is a result of the two pleura, lining the lung cavity, rubbing against each other when inflamed. A pleural rub is often accompanied by pain and and is absent if there is fluid around the lungs between the two pleura (pleural effusion). Another associated term is a pleuropericardial rub which indicates that the pleura are also rubbing against the pericardial lining (heart lining).

Causes of a Pleural Friction Rub

  • Pleuritis (pleurisy)
  • Pleural fibrosis
  • Mesothelioma
  • Lung abscess
  • Pneumonia
  • Pulmonary infarction

Other Abnormal Sounds

  • Pneumothorax Click
    • Air between the two pleura adjacent to the heart causes a clicking sound that is often heard upon contraction of the heart (systole).
  • Stertor
    • This is the crackling or bubbling sound heard over the upper airways as a result of mucus accumulation in these areas.

Related Articles

  1. Causes of Stridor and Wheeze
  2. Noisy Breathing